ACIDOSIS 83 



bears a constant relation (of about 1 :20) to the BHCO 3 . All three con- 

 centrations go up and down together, the blood BIICO 3 fixing the level 

 i>f the H 2 CO 3 , and the latter that of the alveolar CO 2 . Consequently the 

 alveolar CO 2 tension is normally proportional to the blood bicarbonate. 



This proportionality fails when for any reason, such as narcosis of 

 the respiratory center, respiratory stimulus by oxygen want, excitement, 

 or other factors (Van Slyke and Cullen, 1917, p. 299), the ratio BHCO 3 : 

 H 2 CO 3 in the blood plasma becomes variable,' or when the gas exchange 

 in the lungs is mechanically retarded sufficiently to prevent approximately 

 complete CO 2 equilibrium between them, as seems to occur in certain 

 cardiac conditions (Peters and .Barr, 1920). 



The determination is made by determining the CO 2 content of a sample 

 of expired air collected in one of two ways. 



By the technique of Haldane and Priestley (1905) the subject, having 

 been breathing normally, suddenly empties his lungs as completely is 

 possible, the last air expired being analyzed. The CO 2 tension thus deter- 

 mined approximates that of the arterial blood. The simplest technique 

 for collecting and analyzing the air is probably that of Fridericia(a) 

 (1914). The subject expires through a 100 c.c. pipette that can be closed 

 by cocks at both ends. Alkali solution is admitted, which absorbs and dis- 

 places the CO 2 , the c.c. of gas displaced by the solution indicating the 

 percentage of CO 2 . 



With the technique of Plesch (1909) the subject breathes in and out 

 of a bag for 20 or 30 seconds, and the air in the bag is analyzed. The CO 2 

 tension is believed to approximate that of the venous blood. For its de- 

 termination Marriott (6) (1916) has devised a most convenient colorimetric 

 method. The gas from the bag is bubbled through 2 or 3 c.c. of 0.01 N 

 NaOH solution colored with phenolsulphonephthalein. The NaOH is 

 quickly changed to NaHCO 3 , and in 1 or 2 minutes a permanent NaHCO 3 : 

 H 2 CO 3 ratio is established. The H 2 CO 3 , and therefore the hydrion con- 

 centration, is proportionate to the CO 2 content of the air. By comparison 

 with a series of standard tubes over the proper pH range, the CO 2 tension 

 of the air may be estimated from the color of the solution. 



Determination of the Excretion Rate of Ammonia and 



Free Acid 



The sum of ammonia plus titratable acid in the urine represents the 

 excretion of acid in excess of mineral bases. The normal 'excretory reaction 

 of the organism to lowered blood pH or lowered alkaline reserve is an in- 

 crease in excretion of ammonia and titratable acid. Fitz and Van Slyke 

 (1917) and Van Slyke (1918) have shown that in diabetic acidosis the 

 24 hour excretion of ammonia and titratable acid increases approximately 



